The invention pertains to an earth penetrating rotary drill bit that has a hard member at the axial forward end thereof, a hard member, and a bit body.
The expansion of an underground coal mine requires digging a tunnel that initially has an unsupported roof. To provide support for the roof, a rotary drill bit (e.g., a roof drill bit) is used to drill boreholes, which can extend from between about two feet to about (or even greater than) twenty feet, into the earth strata. Roof bolts are affixed within the boreholes and a roof support (e.g., a roof panel) is then attached to the roof bolts. Examples of a conventional roof drill bit with an axial forward slot that carries a blade style hard insert are the KCV4-1RR and KCV4-1 1/32RR Roof Rocket(trademark) drill bits made by Kennametal Inc. of Latrobe, Pa. USA and shown in U.S. Pat. No. 5,172,775 to Sheirer et al.
While the Kennametal Rook Rocket roof drill bits exhibit adequate performance, including a satisfactory penetration rate, it would be desirable to provide a roof drill bit that permits completion of the drilling operation as soon as possible. A roof drill bit that presents at least three leading cutting edges increases the penetration rate due to an increase in the number of the leading cutting edges. Three leading cutting edges, especially with a radial orientation, permits the roof drill bit to advance forward with very little wobble (i.e., side-to-side movement) so as to achieve balanced drilling. Leading cutting edges that terminate short (i.e., at a point radially outward) of the center point of the hard insert define a central open area so as to reduce the amount of low velocity cutting, i.e., the cutting action that occurs nearer to the center point. An increase in the number of the leading cutting edges, the balanced drilling, and the reduction in low velocity drilling each contributes to an increase in the penetration rate of the roof drill bit, which provides for the efficient completion of the drilling operation.
Clogging and stalling may occur when drilling at a higher penetration rate. It would be an advantage to adequately handle and evacuate debris so as to reduce the potential for clogging. It would be an advantage to provide a roof drill bit with a drill bit body that can withstand the stresses inherent during stalling.
Debris impinges upon the roof drill bit that erodes away the steel body so as to increase the possibility of the hard insert becoming dislodged from the body. It would be beneficial to reduce this erosion so as to better maintain the integrity of the braze joint between the hard insert and the bit body.
In the production of the roof drill bit, it would be desirable that the design of the hard insert and the bit body facilitate the correct positioning of the hard insert on the bit body. Furthermore, for such production it would also be desirable if the drill bit body would lend itself to being substantially formed through a process or a combination of processes such as, for example, cold forming or casting.
In one form thereof, the invention is a rotary drill bit for penetrating the earth strata. The drill bit includes a bit body that has an axial forward end wherein a hard insert, which preferably is monolithic, is affixed to the axial forward end thereof. The hard insert presents at least three leading cutting edges.
In still another form thereof the invention is a rotary drill bit for penetrating the earth strata wherein the drill bit has a drill bit body with an axial forward end defined at least in part by spaced apart first and second discrete axial forward surfaces. A hard insert, which preferably is monolithic, is affixed to the axial forward end of the drill bit body so as to form a joint therebetween wherein the joint is defined at least in part by the second discrete axial forward surface.
In yet another form thereof, the invention is a hard member, which preferably is monolithic, that attaches to a drill bit body with a central longitudinal axis so as to form a rotary drill bit. The hard member has a forward surface and a rearward surface. At least three discrete leading cutting edges project from the forward surface of the hard member.
In still yet another form thereof, the invention is an elongate rotary drill bit body that attaches to a hard member, which preferably monolithic, so as to form a rotary drill bit for penetrating earth strata that generates debris. The drill bit body has a peripheral surface and at least one scalloped portion in the peripheral surface. A debris breaker is within the scalloped portion so that debris impinges upon the debris breaker during the penetration operation.
In one form thereof the invention is a rotary drill bit for engaging an earth strata. The drill bit includes a drill bit body with an axial forward end and a hard body that is affixed to the drill bit body at the axial forward end thereof. The hard body carries at least three discrete cutting elements wherein each one of the cutting elements presents a leading cutting edge. The cutting elements are of a hardness greater than the hardness of the hard body and the bit body.
In another form thereof the invention is a roof drill bit body for attachment to a hard member so as to form a rotary drill bit for penetrating earth strata that generates debris wherein the drill bit body comprises a central bore, and a peripheral surface. The peripheral surface contains a trio of debris apertures wherein each aperture is in communication with the central bore.